Electrical windings

ABSTRACT

Windings for electrical inductive apparatus having a plurality of pancake coils arranged in a stack. Each pancake coil has first and second coil sections, the turns of which are radially interleaved. The coil sections of the pancake coils are electrically interconnected to substantially reduce the magnitude of voltage oscillations at the first resonant frequency of the pancake coils and winding, while increasing the voltage between adjacent turns of the interleaved coil sections in a pancake coil to at least three times the steady state voltage across a coil section.

United States Patent lnventor Robert I. VanNice [56] Reference Cited I l N ggg gg UNITED STATES PATENTS P 3,477,052 11/1969 VanNice .1 336/70 Fled 3 493 907 2/1970 s 1 1 336/70 Patented Junel, 1971 teme a. Assignee Westinghouse Electric Corporation Primary Examiner- Thomas J. Kozma Pittsburgh, Pa. AttorneysA T. Stratton, F. E. Browder and D. R. Lackey ABSTRACT: Windings for electrical inductive apparatus having a plurality of pancake coils arranged in a stack. Each pancake coil has first and second coil sections, the turns of which ELECTRICAL WINDINGS are raldlallv nhterleaved. The c051 SECUOES of t helpanciake colllls 1] Claims 9 Drawing Figsare e ectnca y mterconnecte to su stant1a y re uce t e magmtude of voltage osc1llat1ons at the first resonant frequen- U.S. Cl 336/70 cy of the pancake coils and winding, while increasing the volt- Int. Cl. l-l0lf 15/14 age between adjacent turns of the interleaved coil sections in a Field of Search 336/69, 70, pancake coil to at least three times the steady state voltage 186, 187 across a coil section.

l T|5 T3 TI4 T2 Tl3 T1 T12 To Tl5 T3 Tl6 T4 T17 T5 Tl8 T6 L J 1 X T21 T9 T2OT8 Tl9 T7 Tl8 T6 T2l 9 T22 TIO T23 Tll T24 Tl2 PATENTED JUN 119m 3.582.850

' sum 1 or 2 ATTORNEY ELECTRICAL WINDINGS BACKGROUND OF THE INVENTION I. Field of the Invention The invention relates in general to electrical inductive apparatus, such as transformers, and more particularly to windings of the interleaved turn, high series capacitance-type, for such apparatus.

2. Description ofthe Prior Art Electrical inductive apparatus, such as transformers and reactors of the core-form type, commonly utilize a winding constructed of a plurality of spaced, interconnected disc or pancake-type coils. Since the distribution of surge potentials across this type of winding is very nonuniform when using pancake coils of the continuous type, due to the relatively small through or series capacitance of this type of winding compared with the capacitance of the winding to ground, it is common to increase the effective series capacitance of the winding by interleaving. interleaving is accomplished by winding a pancake coil with two or more radially interleaved conductors, each of which forms a coil section, with the various coil sections of the pancake coils of the winding being electrically interconnected to increase the voltage between adjacent turns in the pancake coil..ln other words, while the various coil sections may eventually be connected in series, adjacent coil sections of a pancake coil are connected such that they are from electrically different portions of the winding.

The degree of interleaving, i.e., the magnitude of the potential difference between the turns of radially interleaved coil sections, compared to the voltage across a single coil section, selected for particular application is largely a compromise. The greater the voltage difference between the turns of radially interleaved coil sections, the greater the through or effective series capacitance of the winding. However, increasing the voltage between turns, and thus increasing the voltage stress between adjacent pancake coils, complicates the bringing out of no-load tap connections. Thus, for large power transformers, the degree of interleaving selected is such that the voltage between the turns of interleaved sections is increased to about one or two times the steady state voltage across a single coil section. Single interleaving, i.e., completing the basic interleaving pattern in a single pancake coil by connecting the outer end of one coil section to the inner end of the other coil section, increases the voltage between adjacent turns to the voltage across one coil section, while twin interleaving, i.e., which requires two pancake coils to complete the basic interleaving pattern, increases the voltage between adjacent turns of interleaved coil sections to twice the voltage across one coil section.

While this practical limitation on the maximum degree of interleaving is acceptable in conventional power transformers, when an auxiliary transformer, such as a series transformer, is used with load tap changing power transformers, the auxiliary transformer requires a higher effective series capacitance than the power transformer it is associated with, in order to reduce the surge stress to ground at the point where the two transformers are connected. Even twin interleaved windings do not have a high enough series capacitance to accomplish the desired result. Paralleling a large plurality of twin interleaved windings to secure the desired capacitance for the auxiliary transformer winding is not too practical, with a better approach being to increase the degree of interleaving to provide a voltage between the adjacent turns of interleaved sections which is three, four or more times the voltage across a single coil section.

However, as disclosed in my US. Pat. No. 3,477,052 which is assigned to the same assignee as the present application, increasing the through or series capacitance of a winding may not prevent large magnitude oscillations from occurring when a winding is subjected to a chopped wave or steep front voltage surge. This phenomenon is not explained by the prior art theory related to the distribution constant alpha of the winding. The distribution constant alpha is equal to the square root of the ratio of the capacitance C of the winding to ground to the through or series capacitance C,- of the winding (0: =\C,,/C,,). This theory explains that the smaller the distribution constant alpha. the more uniformly a surge voltage will be distributed across the winding, and the lower the magnitude of voltage oscillations which occur as the voltage distribution changes from capacitive to inductive. While this theory has been found to be accurate for some types ofinterleaving arrangements, other types of interleaving arrangements have been found to produce voltage oscillations upon steep wave front testing, which greatly increases the stress between adjacent pancake coils, with the stress being a maximum near the midpoints of the coil builds. The hereinbefore mentioned copending application teaches how to connect twin interleaved windings to substantially reduce the magnitude of this oscillation. Thus, it would be desirable to be able to connect the coil sections of pancake coils in higher degrees of interleaving, while minimizing the voltage stresses due to oscillations which occur when the winding is subjected to a steep wave front voltage surge. Reducing the magnitude of this oscillator voltage, reduces the amount of insulation required to insulate for the stresses, reducing the size and cost of the apparatus. Merely increasing the amount ofinsulation to withstand the high oscillatory voltages which may occur in certain types of prior art interleaving arrangements is partially self-defeating, as the increased dimensions of the winding insulation resulting from the additional insulation, reduces the through or series capacitance of the winding, increasing the distribution constant alpha of the winding.

SUMMARY OF THE INVENTION Briefly, the present invention discloses electrical windings of the interleaved turn, high series capacitance type, having pancake coils with at least first and second interleaved coil sections, in which the degree of interleaving provides a turnto-turn voltage between interleaved coil sections of more than twice the voltage across a single coil section ofa pancake coil, while minimizing the magnitude of oscillatory voltages which occur upon a steep wave front surge voltage. In one embodiment of the invention, all like positioned coil sections in basic groups of at least four pancake coils are interconnected in numerical sequence. Then, the circuit returns to the first pancake coil of the basic group, to proceed through the remaining coil sections of'the group in numerical sequence. This arrangement substantially reduces the magnitude of voltage oscillations produced upon steep wave front surges, compared with prior art arrangements where the circuit proceeds completely through the basic group of pancake coils in sequence, but by alternating the coil sections from pancake coil to pancake coil, and then returning to the first pancake coil of the basic group to again proceed through the pancake coils in numerical sequence, via the remaining sections, which again alternate coil sections from pancake coil to pancake coil.

Another embodiment of the invention, specifically applicable to obtaining degrees of interleaving which are even multiples of a coil section voltage, provides a series circuit through a basic group of an even number of pancake coils, starting with four, wherein a series circuit traverses like positioned coil sections of the first pancake coil of the group, the remaining odd numbered pancake coils of a group in numerical sequence, the last pancake coil of the group, and then the even numbered pancake coils of the group in reverse numerical sequence. The circuit then returns to the first pancake coil of the basic group and repeats this same sequence through the remaining coil sections of the group.

In still another embodiment of the invention, specifically applicable to obtaining degrees of interleaving which are odd multiples of a coil section voltage, starting with a multiple of three, provides a series circuit through a basic group of six or more coils, wherein the series circuit traverses like coil sections of the first and remaining odd numbered pancake coils of the group in numerical sequence, it then returns to traverse the remaining sections of the first and remaining odd numbered pancake coils or the group in numerical sequence, it then returns to traverse like coil sections of the even numbered pancake coils in numerical sequence, and then returns to traverse the remaining coil sections of the even numbered pancake coils in numerical sequence. The first traverse of the even and odd number pancake coils are made through like positioned coil sections.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of the invention will become more apparent when considered in view of the following detailed description of exemplary embodiments thereof, taken with the accompanying drawings, in which:

FIG. I is a partial sectional elevation of an electrical winding for a transformer or reactor, constructed according to a first embodiment of the invention;

FIG. 1A is a schematic representation of the winding shown in FIG. 1;

FIG. 2 is a diagrammatic view illustrating an electrical winding constructed according to another embodiment of the invention;

FIG. 2A is a schematic representation of the winding shown in FIG. 2;

FIG. 3 is a graph which plots the stress between a group of pancake coils produced by chopped wave impulse testing, for windings constructed according to the teachings of the prior art, and according to the teachings of the invention illustrated in FIGS. 1 and 2;

FIG. 4 is a diagrammatic view of an electrical winding constructed according to another embodiment of the invention;

FIG. 4A is a schematic representation of the winding shown in FIG. 4;

FIG. 5 is a diagrammatic view of the winding constructed according to still another embodiment of the invention; and

FIG. 5A is a schematic representation of the winding shown in FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, and FIG. I in particular, there is shown a partial sectional elevation of electrical inductive apparatus 10, such as a transformer or reactor, having a magnetic core 12 and a winding 14 which has a plurality of pancake coils l6, 18, and 22 constructed and connected according to a first embodiment of the invention. Additional windings are not shown, in order to simplify the drawing.

Electrical inductive apparatus I0 may be a series transformer used for tap changing, an autotransformer, or any other type of electrical inductive apparatus where it is desirable to increase the degree of interleaving of interleaved type pancake coils beyond that of twin interleaving. Since each phase of a .polyphase transformer or reactor would have similarly constructed windings, only a single phase is illustrated in FIG. 1. Further, only a sufficient number of pancake coils, and turns per pancake coil are shown in FIG. 1, and the remaining FIGS. in order to adequately illustrate the invention. It will be understood that the windings illustrated in the drawings may have any desired number of pancake coils, and turns per pancake coil.

More specifically, winding I4 includes a plurality of pancake coils 16, I8, 20 and 22, which are spaced axially apart in a stacked arrangement about the axis 24 of a leg portion 26 of magnetic core 12. The plurality of pancake coils of winding 14 are constructed to provide a high series capacitance, interleaved turn type winding, having a single series circuit between line terminal 28 at the start of winding 14, and a terminal at the finish of the winding (not shown), which may be a line or a neutral terminal, depending upon the specific construction and application of apparatus 10.

Each of the pancake coils l6, I8, 20 and 22 have a plurality of conductor turns formed of at least first and second electrical conductors or strands spirally wound together about the common axis 24, to provide first and second coil sections I and II, respectively, each having inner and outer ends, the turns of which are radially interleaved with one another in substantially the same plane. The inner ends are termed the start," and the outer ends the finish" of a coil section, regardless of where the electrical circuit first enters the coil section. The conductor turns are insulated from one another in a manner well known in the art, with the insulation not being shown in order to clarify the drawings. Coil sections I and II are best illustrated in the schematic diagram of high voltage winding 14 shown in FIG. IA. The two interleaved sections I and II of each pancake coil are shown slightly offset from one another in the schematic diagram of FIG. IA, in order to more clearly denote the different radial locations of the two sections in a pancake coil.

In the embodiment of the invention shown in FIG. I, quadruple interleaving is illustrated, which requires a basic group of four adjacent pancake coils, and provides a voltage difference between adjacent conductor turns of the interleaved coil sections which is four times the voltage across one coil section of a pancake coil. This voltage difference is illustrated in the schematic representation of winding 14, shown in FIG. 1A, with the voltage across one coil section being equal to one unit of voltage, starting at the line terminal 28.

The line terminal 23 is connected to the end of the outermost turn T0 of one of the coil sections, which in this instance is coil section II, and the pancakes are interconnected to direct the circuit through like located coil sections in numerical sequence. For example, if the pancake coils of the group are numbered I...n, with pancake coil 16 being the first pancake coil and pancake coil 22 being the nth pancake coil, the circuit will traverse like positioned sections of all of the pancake coils in numerical sequence, and then return to the first pancake coil and traverse all of the remaining like positioned coil sections.

More specifically, if the circuit first enters the outer turn of coil section II, the circuit spirals inwardly through pancake coil 16, appearing at every other turn, with the turns being given the letter T and a number which indicates the position of the turn in the winding relative to the line terminal 28. At the end of the innermost turn of coil section II in pancake coil 16, the circuit enters coil section II of pancake coil 18 via startstart connector 30, and the circuit then spirals outwardly, appearing at every other turn until reaching the end of its outermost turn T6. The circuit then proceeds to the end of the outermost turn of coil section II of pancake coil 20, via finishfinish connector 32, it spirals inwardly through pancake coil 20 to the end of the innermost turn of coil section II, it proceeds to the end of the innermost turn of coil section II of pancake coil 22 via start-start connector 34, and spirals outwardly until reaching turn T12 at the end of the outermost turn of coil section II of pancake coil 22. The circuit then returns to the first pancake coil 16 via connector 36, and traverses coil section I of each of the pancake coils of the group in numerical sequence. Coil section I of pancake coil I6 is connected to coil section I of pancake coil I8 via start-start connector 31, coil section I of pancake coil 18 is connected to coil section I of pancake coil 20 via finish-finish connector 33, and coil section I of pancake coil 20 is connected to coil section I of pancake coil 22 via start-start connector 35. The end of the outermost turn of coil section I of pancake coil 22 then proceeds via connector 37 to the next basic group of pancake coils, where the sequence hereinbefore described would be repeated.

Twelve pancake coils numbered I through I8, starting from the line terminal, were interconnected as taught by FIG. I, forming three basic groups of four, each quadruply interleaved, to provide four times the voltage between adjacent turns as appears across a single coil section. The interconnected coils were then tested with a standard chopped wave impulse voltage, with the results of the tests being plotted in the graph of FIG. 3. The abscissa of the graph is numbered to indicate pairs of coils adjacent the line end of the winding, and the ordinate indicates the percent of the peak applied voltage which appeared between each pair of adjacent pancake coils, at substantially the midpoints of their radial builds, which is the point of the maximum oscillatory voltage. Curve 40 connects the voltages measured between adjacent pairs of pancake coils, when he coils were connected as taught by the embodiment of the invention shown in FIG. 1, with the curve starting at about 48 percent of the applied voltage between pancake coils l and 2, dropping as low as about 25 percent of the applied voltage between pancake coils 2 and 3, and rising to about 52 percent of the applied voltage between pancake coils 5 and 6.

Reconnecting the same pancake coils as taught by the prior art, to alternate coil sections from pancake coil to pancake coil, provided the results shown by curve 42 in FIG. 3. It will be noted that the stresses are substantially higher with this type of connection than with the connection shown in FIG. 1, starting at about 55 percent of the applied voltage between pancake coils I and 2, increasing to about 75 percent of the applied voltage between pancake coils 3 and 4. Thus, connecting the pancake coils according to the teachings of the invention shown in FIG. 1, provides a substantial reduction in surge stresses between adjacent pancake coils, which occurs at the first resonant frequency of the assembly, typically between 0.5 and 2 megahertz, depending upon the dimensions of the pancake coils.

It will be obvious that the teachings of the invention shown in FIGS. 1 and 1A may be extended to any number of pancake coils to provide any desired degree of interleaving. In other words, the pancake coils would be interconnected such that the circuit would proceed completely through the basic group of pancake coils via the like positioned coil sections, with the circuit proceeding through the pancake coils in numerical sequence, and then the circuit would return to the first pancake coil of the basic group and proceed through the pancake coils in numerical sequence, via the remaining like positioned coil sections. While it is not absolutely essential, in general it has been found to be preferable that each basic group of coils include an even number of pancake coils.

The stresses between adjacent pancake coils in quadruply interleaved windings may also be reduced, by connecting the pancake coils I6, 18, 20 and 22 as illustrated in FIGS. 2 and 2A, which, in effect, places the last pancake of the group shown in FIG. 1, between the first and second pancake coils of the group. Like reference numerals indicate like components in FIGS. 1 and 2, and like reference numerals except for a prime mark indicate like functions but slightly different structure.

More specifically, FIGS. 2 and 2A are diagrammatic and schematic views of a winding 14', in which the circuit proceeds through a basic group of four pancake coils via like coil sections of the first pancake coil, the third pancake coil, the four pancake coil, and then the second pancake coil, with the circuit then returning to the first pancake coil and repeating this sequence through the remaining like sections of the pancake coils. In other words, if the circuit first enters the end of the outer turn of the second coil section II, the circuit will spiral inwardly through this section until reaching the end of its innermost turn T3 and will then be connected to coil section II of the third pancake coil 20 via start-start connector 30'. This circuit spirals outwardly through pancake coil 20 until reaching the end of its outermost turn T6 and it then proceeds to the fourth and last pancake coil of the basic group, pancake coil 22, via finish-finish connector 32'. The circuit spirals inwardly until reaching the end of the innermost turn of coil section II of pancake coil 22, and then proceeds to coil section II of the second pancake coil of the group, pancake coil 18, via start-start connector 34', and the circuit spirals outwardly through pancake coil 18 until reaching the end of the outermost turn T12 of coil section II. The circuit then proceeds back to the first pancake coil 16, entering the end of the outermost turn of coil section I via finish-finish connector 36'. The circuit then spirals inwardly through coil section I of pancake coil 16, it continues to the third pancake coil 20 via start-start connector 31, which enters the innermost turn of coil section I of pancake coil 20, it spirals outwardly through pancake coil 20 and enters the end of the outermost turn T18 of coil section I of pancake coil 20, it spirals outwardly through pancake coil 20 and enters the end of the outermost turn T18 of coil section I in the fourth pancake coil 22 via finish-finish connector 33', it spirals inwardly until reaching the end of the innermost turn of this section and enters section I of the second pancake coil 18 via start-start connector 35, and then spirals outwardly to the end of this section, which completes the basic interleaving pattern. The circuit then proceeds to the next basic group of pancake coils via connector 37.

Interconnecting the same pancake coils used to test the embodiment of the invention shown in FIG. I, and the prior art arrangement, to incorporate the teachings of the invention shown in FIGS. 2 and 2A, and testing the interconnected coils with a standard chopped wave impulse voltage, provided the results shown in curve 44 of FIG. 3. The voltage stress starts at about 30 percent of the applied voltage between the first pair of pancake coils, rises to about 60 percent of the applied voltage between pancake coils 4 and 5, and drops to about 50 percent of the applied voltage between pancake coils 5 and 6.

The teachings of the embodiment of the invention shown in FIGS. 2 and 2A may be extended to higher, even numbered degrees ofinterleaving. Broadly, the interleaving arrangement shown in FIG. 2 teaches connecting the coil sections of a plurality of pancake coils such that the circuit traverses like coil sections of the first pancake coil of the basic group, the remaining odd numbered pancake coils of the group in numerical sequence, the last pancake coil of the basic group, and then the even numbered pancake coils in reverse numerical sequence. The circuit then returns to the first pancake coil of the group to follow this same sequence through the remaining coil sections. FIGS. 4 and 4A are diagrammatic and schematic views, respectively, of a winding 50 which is connected according to the broad teachings of the embodiment of the invention shown in FIG. 2, to provide a voltage difference between adjacent turns ofinterleaved coil sections which is six times the steady state voltage across one of the coil sections of a pancake coil, which may be termed sextuplet interleaving.

More specifically, winding 50 shown in FIGS. 4 and 4A requires a basic group of six pancake coils, 52, 54, 56, 58, 60 and 62. Each of the pancake coils have first and second coil sections I and II, respectively, with the line terminal 64 being connected to the end of the outermost turn of one of the coil sections of the first pancake coil 52, such as the outermost turn of coil section II, advancing from the innermost turn of coil section II of pancake coil 52 to the innermost turn of coil section II of the third pancake coil 56 via start-start connector 66, advancing from the end of the outermost turn of coil section II of pancake coil 56 to the end of the outermost turn of coil section II of the fifth pancake coil 60 via finish-finish connector 68, advancing from the innermost turn of coil section II of pancake coil 60 to the innermost turn of coil section II of pancake coil 62, the last pancake of the basic group, via startstart connector 70, returning to the fourth pancake coil 58 via finish-finish connector 72, which enters coil section II of pancake coil 58, continuing from the innermost turn of coil section II of pancake coil 58, via start-start connector 74, to the end of the innermost turn of coil section II of the second pancake coil 54, and then returning to the first pancake coil, entering the end of the outermost turn of coil section I of pancake coil 52 via finish-finish connector 76. The circuit then continues through the pancake coils, in the hereinbefore enumerated sequence, following coil sections I of these pancake coils. The first and third pancake coils are interconnected via start-start connector 78, the third and fifth pancake coils are interconnected via finish-finish connector 80, and the fifth and sixth pancake coils are interconnected v'ia start-start connector 82. The circuit then proceeds back toward the start of the basic group, interconnecting the last pancake coil 62 to the fourth pancake coil 58 via finish-finish connector 84, and the fourth pancake coil 58 to the second pancake coil 54 via start-start connector 86, which then completes the interleaving arrangement. Conductor 88 leaves the outermost turn of coil section 1 of pancake coil 54 and continues to the next basic group of pancake coils.

Up to this point, the embodiments of this invention have illustrated interleaving arrangements which provide degrees of interleaving which are even multiples of the voltage across a single coil section of the pancake coil. It is also possible to obtain degrees of interleaving which are odd multiples of a coil section voltage, with FIGS. 5 and 5A being diagrammatic and schematic views, respectively, of a winding 100 constructed according to this embodiment of the invention. In the specific embodiment shown in FIGS. 5 and 5A, triple interleaving is illustrated, but by following the broad teachings of this embodiment any odd numbered degree of interleaving may be achieved. Broadly, this embodiment requires twice as many pancake coils each having first and second radially interleaved coil sections 1 and ll, respectively. The coil sections are interconnected to direct the circuit through like coil sections of the first and remaining odd numbered pancake coils of the group in numerical sequence, the circuit returns to traverse the remaining coil sections of the first and odd numbered pancake coils of the group in numerical sequence, the circuit then enters the second pancake coil via the same coil section first traversed in the first pancake coil, and this and similar sections of the event numbered pancake coils are traversed in numerical sequence through the basic group, and then the circuit returns to the second pancake coil and traverses the remaining sections of the second and remaining even numbered pancake coils, in numerical sequence through the basic group.

Specifically, the arrangement shown in FIGS. 5 and 5A provides a steady state difference of potential between adjacent turns of interleaved coil sections of a pancake coil which is equal to three times the voltage across a single coil section, as indicated in the schematic representation of the winding in FIG. 5A. Winding 100 of FIGS. 5 and 5A includes six pancake coils per basic group, 102, 104, 106, 108, 110 and 111, with each pancake coil having first and second radially interleaved sections l and ll, indicated in FIG. 5A. The pancake coils are disposed in stacked, spaced relation about a common center line 112, with the pancake coils being numbered numerically 1...n, with the first pancake coil starting with pancake coil 102 adjacent like terminal 114, and with pancake coil 111 being the nth pancake coil. The line terminal 114 is connected to the end of the outermost turn of one of the coil sections of the first pancake coil 102, such as coil section ll, and the circuit then proceeds through coil section II of pancake coil 102, and similar coil sections of the remaining odd numbered pancake coils, in numerical sequence through the group. Coil section ll of pancake coil 102 is connected to coil section ll of the third pancake coil 106, via start-start connector 166, coil section ll of pancake coil 106 is connected to coil section ll of the fifth pancake coil 110, via finish-finish connector 118, and then the circuit returns to the first pancake coil 102 via connector 120, proceeding through coil section I of pancake coil 102, advancing to coil section I of pancake coil 106 via start-start connector 122, and then entering coil section 1 of pancake coil 110 via finish-finish connector 124, which completes the interleaving of the first and remaining odd numbered pancakes. The circuit then proceeds from coil section 1 of pancake coil 110 to coil section ll of the second pancake coil 104, via start-start connector 126, coil sections ll of pancake coils 104 and 108 are interconnected via finish-finish connector 128, and the fourth and sixth pancake coils have their coil sections ll interconnected via start-start connector 130. The circuit then returns to the second pancake coil via connector 132 which enters coil section I of pancake coil 104, coil sections l ofthe second and fourth pancake coils 104 and 106, respectively,

are interconnected via finish-finish connector 134, and coil sections 1 of the fourth and sixth pancake coils 108 and 111, respectively, are interconnected via start-start connector 136. The circuit then leaves the outermost turn of coil section I of pancake coil Ill via connector 138, which is connected to the next basic group of pancake coils.

While the various embodiments of the invention have been shown and described with two radially interleaved coil sections per pancake coil, with the two coil sections eventually being connected to provide a single series circuit through the winding, it will be obvious that the teachings may be extended to a larger plurality of coil sections per pancake coil, to provide more than one circuit through the winding, which circuits are eventually connected in parallel. Further, the embodiments have been illustrated with as few top-to-bottom connections as possible, i.e., connections which extend between the innermost and outermost turns of coil sections, which in general requires that the pancakes be interconnected with start-start, finish-finish connections. However, it is to be understood that the teachings of the invention may be extended to interconnect all of the pancake coils with finish-start connections. Finish-start connections increase the number of topto-bottom connections, but it simplifies the construction of the pancake coils as they may be all machine wound. With finish-finish, start-start connections, the coils in which the circuit spirals inwardly are machine wound and then broken down and rewound by hand to reverse the direction in which the conductors spiral in these pancake coils in order to provide a uniform direction of instantaneous current in all of the coils and thus an additive magnetomotive force, without the necessity of severing the conductors. It will be noted that in the embodiment of the invention shown'in FIGS. 1 and 1A, that the circuit spirals inwardly in the odd numbered pancake coils ofa group, and outwardly in the remaining pancake coils, while in the remaining embodiments of the invention, the circuit spirals inwardly in the first pancake coil and outwardly in the next pancake coil, and then the sequence reverses to spiral outwardly in the next pancake coil and inwardly in the next pancake coil. The direction of the instantaneous current flow in each pancake coil is indicated by an arrow in the schematic representations of the various windings.

In summary, there has been disclosed new and improved electrical windings of the interleaved turn, high series capacitance-type, in which the degree of interleaving may be extended beyond that of the twin interleaved winding, while insuring that the oscillatory voltage buildup at the first resonant frequency of the winding will be attenuated.

1 claim as my invention:

1. A winding for electrical inductive apparatus, comprising:

a plurality of at least four pancake coils arranged in a stack,

each of said pancake coils having first and second radially interleaved coil sections,

means interconnecting predetermined like coil sections of adjacent pancake coils, providing a first series path having first and second ends which successively traverses all of the predetermined like coil sections of the pancake coils of the stack,

means interconnecting the remaining coil sections of adjacent pancake coils, providing a second series path having first and second ends which successively traverses all of the pancake coils of the stack,

and means connecting the second end of one of the series paths to the first end of the other ofthe series paths.

2. The winding of claim 1 wherein the plurality of pancake coils is an even numbered plurality.

3. The winding of claim 1 herein the first and second series paths spiral inwardly in alternate pancake coils and outwardly in the remaining pancake coils.

4. The winding of claim 1 wherein the pancake coils are successively connected with start-start, finish-finish connections.

5. A winding for electrical inductive apparatus, comprising:

a plurality of at least four pancake coils arranged in a stack and numbered 1...n, each of said pancake coils having first and second radially interleaved coil sections, each of which have inner and outer ends,

means sequentially interconnecting like coil sections of the first pancake coil, the remaining odd numbered pancake coils in advancing numerical sequence, the last pancake coil n, and the even numbered pancake coils in reverse numerical sequence, to provide a first series path having first and second ends,

means sequentially interconnecting the like remaining coil sections of the first pancake coil, the remaining odd numbered pancake coils in advancing numerical sequence, the last pancake coil n, and the even numbered pancake coils in reverse numerical sequence, to provide a second series path having first and second ends,

and means interconnecting the second end of one of the series paths to the first end of the other of the series paths. 6. The winding of claim wherein the plurality of pancake coils is an even numbered plurality.

7. The winding of claim 5 wherein the plurality of pancake coils is an even numbered plurality, and the pancake coils are divided into a plurality of pairs of first and second adjacent pancake coils, wherein the series paths spiral inwardly and outwardly in the first and second coils, respectively, of alternate pairs of coils, and outwardly and inwardly in the first and second coils, respectively, of the remaining pairs of pancake coils.

8. A winding for electrical inductive apparatus, comprising: a plurality of at least six pancake coils arranged in a stack and numbered 1...n,

each of said pancake coils having first and second radially interleaved coil sections, each having inner and outer ends,

means sequentially interconnecting like coil sections of the first and remaining odd numbered pancake coils in advancing numerical sequence, to provide a first path through the odd numbered pancake coils having first and second ends,

means sequentially interconnecting the remaining coil sections of the first and remaining odd numbered pancake coils in advancing numerical sequence, to provide a second path through the odd numbered pancake coils having first and second ends,

means interconnecting the second end of the first path through the odd numbered pancake coils to the first end of the second path through the odd numbered pancake coils, means sequentially interconnecting like coil sections of the even numbered pancake coils in advancing numerical sequence, to provide a first series path through the even numbered pancake coils having first and second ends,

means sequentially interconnecting the remaining coil sections of the even numbered pancake coils in advancing numerical sequence, to provide a second path through the even numbered pancake coils having first and second ends,

means interconnecting the second end of the first path through the even numbered pancake coils to the first end of the second path through the even numbered pancake coils,

and means interconnecting the second end of the second path through the odd numbered pancake coils to the first end of the first path through the even numbered pancake coils, to provide a single series path through the winding.

9. The winding of claim 8 wherein the plurality of pancake coils is an even numbered plurality.

10. The winding of claim 8 wherein the plurality of pancake coils is an even numbered plurality, and the pancake coils are divided into a plurality of pairs of first and second pancake coils, with the series circuit spiralling inwardly and outwardly in the first and second coils, respectively, of alternate pairs of coils, and outwardly and inwardly in the first and second coils,

res ectively, of the remuiningpairs of pancake coils.

l. The winding of claim wherein the first paths through both the even and odd numbered pancake coils occupy like numbered coil sections. 

1. A winding for electrical inductive apparatus, comprising: a plurality of at least four pancake coils arranged in a stack, each of said pancake coils having first and second radially interleaved coil sections, means interconnecting predetermined like coil sections of adjacent pancake coils, providing a first series path having first and second ends which successively traverses all of the predetermined like coil sections of the pancake coils of the stack, means interconnecting the remaining coil sections of adjacent pancake coils, providing a second series path having first and second ends which successively traverses all of the pancake coils of the stack, and means connecting the second end of one of the series paths to the first end of the other of the series paths.
 2. The winding of claim 1 wherein the plurality of pancake coils is an even numbered plurality.
 3. The winding of claim 1 herein the first and second series paths spiral inwardly in alternate pancake coils and outwardly in the remaining pancake coils.
 4. The winding of claim 1 wherein the pancake coils are successively connected with start-start, finish-finish connections.
 5. A winding for electrical inductive apparatus, comprising: a plurality of at least four pancake coils arranged in a stack and numbered 1...n, each of said pancake coils having first and second radially interleaved coil sections, each of which have inner and outer ends, means sequentially interconnecting like coil sections of the first pancake coil, the remaining odd numbered pancake coils in advancing numerical sequence, the last pancake coil n, and the even numbered pancake coils in reverse numerical sequence, to provide a first series path having first and second ends, means sequentially interconnecting the like remaining coil sections of the first pancake coil, the remaining odd numbered pancake coils in advancing numerical sequence, the last pancake coil n, and the even numbered pancake coils in reverse numerical sequence, to provide a second series path having first and second ends, and means interconnecting the second end of one of the series paths to the first end of the other of the series paths.
 6. The winding of claim 5 wherein the plurality of pancake coils is an even numbered plurality.
 7. The winding of claim 5 wherein the plurality of pancake coils is an even numbered plurality, and the pancake coils are divided into a plurality of pairs of first and second adjacent pancake coils, wherein the series paths spiral inwardly and outwardly in the first and second coils, respectively, of alternate pairs of coils, and outwardly and inwardly in the first and second coils, respectively, of the remaining pairs of pancake coils.
 8. A winding for electrical inductive apparatus, comprising: a plurality of at least six pancake coils arranged in a stack and numbered 1...n, each of said pancake coils having first and second radially interleaved coil sections, each having inner and outer ends, means sequentially interconnecting like coil sections of the first and remaining odd numbered pancake coils in advancing numerical sequence, to provide a first path through the odd numbered pancake coils having first and second ends, means sequentially interconnecting the remaining coil sections of the first and remaining odd numbered pancake coils in advancing numerical sequence, to provide a second path through the odd numbered pancake coils having first and second ends, means interconnecting the second end of the first path through the odd numbered pancake coils to the first end of the second path through the odd numbered pancake coils, means sequentially interconnecting like coil sections of the even numbered pancake coils in advancing numerical sequence, to provide a first series path through the even numbered pancake coils having first and second ends, means sequentially interconnecting the remaining coil sections of the even numbered pancake coils in advancing numerical sequence, to provide a second path through the even numbered pancake coils having first and second ends, means interconnecting the second end of the first path through the even numbered pancake coils to the first end of the second path through the even numbered pancake coils, and means interconnecting the second end of the second path through the odd numbered pancake coils to the first end of the first path through the even numbered pancake coils, to provide a single series path through the winding.
 9. The winding of claim 8 wherein the plurality of pancake coils is an even numbered plurality.
 10. The winding of claim 8 wherein the plurality of pancake coils is an even numbered plurality, and the pancake coils are divided into a plurality of pairs of first and second pancake coils, with the series circuit spiralling inwardly and outwardly in the first and second coils, respectively, of alternate pairs of coils, and outwardly and inwardly in the first and second coils, respectively, of the remaining pairs of pancake coils.
 11. The winding of claim 8 wherein the first paths through both the even and odd numbered pancake coils occupy like numbered coil sections. 